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Can somene explain why strenous exercise is considered to be diffusion limited?
I always thought it was perfusion limited because if the Cardiac Output is fast (due to tachycardia during exercise), then there will not be enough time for equilibration during exchange.
This one always confuses me so can please someone explain thoroughly the concept here. THANKS.
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this is an interesting question. I'm confused too. co-ask, thanks!
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normally the capillaries are completely saturated with o2 by the time it reaches half the length of a capillary thats the reason even if you supply more o2 there is no use since your blood is completely saturated,
but when you exercise there is increased surface area due to recruitment of new capillaries in less perfused areas in the lungs becuase of increased cardiac output so there is increased perfusion that would help us get more o2 ............but (here lies you answer) now the cardiac out put exceeds the capacity of o2 supply you have more blood to be saturated then you have ventilation so now it is diffusion limited in short you need more O2.
. (decreased ventilation might be due to raised respiratory rate but decreased depth of respiration reducing the amount of time available to saturate all the blood.
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the increased cardiac output shortens the time available for diffusion and can result in incomplete transfer of oxygen; i.e., a diffusion limitation.
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wow, got it. thanks a lot.
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awesome reddy.... so it is basically what i was thinking about equilibration, but in respect to diffusion instead of perfusion.. if there is not enough time for DIFFUSION to occur, than it is the speed of blood flow that LIMITS the equilibration, therefore it is considered DIFFUSION LIMITED, not perfusion limited,since it is not a matter of getting the blood supply there, it is a matter of having it stay long enough to pick up a sufficient amount of O2.
surface area is also important here, as you mentioned reddy...
this should remind us of the Diffusion formula
Diffusion (Vgas) = SA/ T x D x (p1-p2)
SA- surface area
T- thickness
D- diffusion solubilty constant of that gas
p1-p1 .. pressure gradient across the alv/capill membrane
so if we inc the SA (by recruitment of more capillaries) then we incr the diffusion, since more alveoli are opening up now and taking part in O2 exchange.
i hope i got it right this time.
Thanks for all your input.
